To answer this question, we need to understand Chargaff's rule, which pertains to the base pairing in DNA.
Chargaff's rule states that in any given DNA molecule:
1. The amount of adenine (A) is equal to the amount of thymine (T).
2. The amount of cytosine (C) is equal to the amount of guanine (G).
Let's examine the four given options in light of Chargaff's rule:
Option A: A = T ; C = G
- This option matches precisely with Chargaff's rule, as it states that adenine pairs with thymine and cytosine pairs with guanine.
Option B: A = C ; T = G
- This option is incorrect because adenine does not pair with cytosine, and thymine does not pair with guanine.
Option C: A = G ; T = U
- This option is also incorrect for a couple of reasons:
- Adenine does not pair with guanine (A = G).
- Thymine is in DNA, and uracil (U) is in RNA, not DNA. In DNA, adenine pairs with thymine (A = T).
Option D: A = U ; C = G
- This option is incorrect since:
- Adenine pairs with uracil (A = U) only in RNA, not DNA.
- Additionally, in DNA, adenine pairs with thymine (A = T), not uracil.
Based on this analysis, the correct option should be:
Option A: A = T ; C = G
Thus, according to Chargaff's rule, base pairing in DNA corresponds to option A.
